anonymous-function

问题 This question already has an answer here: JavaScript closure inside loops – simple practical example 44 answers I\'ve been trying to assign a function to onclick event of a dynamically created \"a\" tag in JavaScript. All of the tags are created in a loop as follows: for ( var i = 0; i < 4; i++ ) { var a = document.createElement( \"a\" ); a.onclick = function( ) { alert( i ) }; document.getElementById( \"foo\" ).appendChild( a ); } The alerted value for all four links is always \"4\". Pretty

问题 Part of a website\'s JSON response had this (... added for context): {..., now:function(){return(new Date).getTime()}, ...} Is adding anonymous functions to JSON valid? I would expect each time you access \'time\' to return a different value. 回答1: No. JSON is purely meant to be a data description language. As noted on http://www.json.org, it is a "lightweight data-interchange format." - not a programming language. Per http://en.wikipedia.org/wiki/JSON, the "basic types" supported are: Number

问题 In ES6 we can do anonymous class: var entity = class { } But we can also instantiate it: var entity = new class { constructor(name) { this.name = name; } getName() { return this.name; } }(\'Foo\'); console.log(entity.getName()); // Foo What is done behind it, what advantage will it bring and what caveats will it also bring? 回答1: Anonymous class instance — is it a bad idea? Yes, a very bad one. Just as bad as new function() { … } was in ES5. This writing style leads to the creation of a new

问题 function doSomethingWith(param) { document.body.addEventListener( \'scroll\', function() { document.write(param); }, false ); // An event that I want to remove later } setTimeout( function() { document.body.removeEventListener(\'scroll\', HANDLER ,false); // What HANDLER should I specify to remove the anonymous handler above? }, 3000 ); doSomethingWith(\'Test. \'); 回答1: You can't. You have to use a named function or store the reference somehow. var handler; function doSomethingWith(param) {

问题 Possible Duplicate: Location of parenthesis for auto-executing anonymous JavaScript functions? Sometimes I see: (function() { ... }()); and sometimes I see: (function() { ... })(); I see both forms with and without arguments. They both execute the anonymous function. Is there a difference between the two forms? Are there any compelling reasons to use one form over the other? 回答1: There is no practical difference in those two forms, but from a grammatical point of view the difference between

问题 Why is this in an anonymous function undefined when using javascript in strict mode? I understand why this could make sense, but I couldn\'t find any concrete answer. Example: (function () { \"use strict\"; this.foo = \"bar\"; // *this* is undefined, why? }()); Test in a fiddle: http://jsfiddle.net/Pyr5g/1/ Check out the logger (firebug). 回答1: It's because, until ECMAscript 262 edition 5, there was a big confusion if people who where using the constructor pattern , forgot to use the new

问题 I was reading some posts about closures and saw this everywhere, but there is no clear explanation how it works - everytime I was just told to use it...: // Create a new anonymous function, to use as a wrapper (function(){ // The variable that would, normally, be global var msg = \"Thanks for visiting!\"; // Binding a new function to a global object window.onunload = function(){ // Which uses the \'hidden\' variable alert( msg ); }; // Close off the anonymous function and execute it })(); Ok

问题 Considering the following code snippet : # directorys == {\'login\': <object at ...>, \'home\': <object at ...>} for d in directorys: self.command[\"cd \" + d] = (lambda : self.root.change_directory(d)) I expect to create a dictionary of two function as following : # Expected : self.command == { \"cd login\": lambda: self.root.change_directory(\"login\"), \"cd home\": lambda: self.root.change_directory(\"home\") } but it looks like the two lambda function generated are exactly the same : #

问题 I was recently comparing the current version of json2.js with the version I had in my project and noticed a difference in how the function expression was created and self executed. The code used to wrap an anonymous function in parenthesis and then execute it, (function () { // code here })(); but now it wraps the auto-executed function in parenthesis. (function () { // code here }()); There is a comment by CMS in the accepted answer of Explain JavaScript’s encapsulated anonymous function

问题 Summary Can you explain the reasoning behind the syntax for encapsulated anonymous functions in JavaScript? Why does this work: (function(){})(); but this doesn\'t: function(){}(); ? What I know In JavaScript, one creates a named function like this: function twoPlusTwo(){ alert(2 + 2); } twoPlusTwo(); You can also create an anonymous function and assign it to a variable: var twoPlusTwo = function(){ alert(2 + 2); }; twoPlusTwo(); You can encapsulate a block of code by creating an anonymous